Method of generating power

ABSTRACT

This document describes an improved method and apparatus for recycling energy in counterflow heat exchange and distillation. The basis of the invention is transferring heat with thin sheets of material having extensive surface area relative to the flow rate through the system. A distillation apparatus (11 and 12), a counterflow heat exchanger (11), a clothes dryer (FIG. 9), a power generator (FIG. 12), and other embodiments of the invention are described.

This is a division of application Ser. No. 038,601 filed Apr. 15, 1987,(now U.S. Pat. No. 4,769,113) which is a division of application Ser.No. 604,023 filed Apr. 26, 1984 (now U.S. Pat. No. 4,671,856) accordedthe benefit of the filing date of Sept. 2, 1982 of the PCT applicationSer. No. PCT/US82/01191.

DESCRIPTION BACKGROUND OF THE INVENTION

This invention is a method and apparatus for heat exchange. Its mainapplications are in distillation and in counterflow heat exchange.Various models of the invention distill water, distill fuel alcohol,concentrate juices and brines, separate toxic chemicals from industrialwastewater, remove moisture from grains or clothing, exchange heatbetween liquids, and generate electrical power. The fundamental designstrategy of the invention is to move heat over a large surface arearelative to the flow rate through the system. This background sectionidentifies some of the problems addressed by the invention and describesthe conventional solutions.

Water Supply Global water supply

Our planet's ecosystem includes about 326 billion cubic miles (1trillion, 336 billion cubic kilometers) of water. Only a tiny fractionof this water is available for drinking or irrigation. Ninety-sevenpercent lies in the oceans, too salty for human life support. Anothertwo and a half percent is frozen in the polar ice caps. For drinking andirrigation we rely almost entirely on fresh water--less than half of 1%of the global water supply. A billion people, or one-fourth of us, lackclean drinking water. Contaminated drinking water is involved in 80% ofall human illness and disease, according to the World HealthOrganization. Gastroenteritis, dysentery, cholera, and other waterbornediseases claim ten million lives each year. The United Nations hasdeclared the 1980's the International Drinking Water and SanitationDecade and set an ambitious goal: to supply clean drinking water for allpeople by 1990. To accomplish this goal the United Nations will have tobring new sources of clean drinking water to half a million people eachday (on the average) until the end of the decade. Dr. Peter Bourne, U.N.coordinator, has predicted that abundant clean water will "totallyrevolutionize the life style of rural people in every country of theworld."

Water supply in the United States

The United States draws on groundwater resources and surface waterresources in roughly equal measure. Most Americans grew up with plentyof safe, clean water available at the turn of a tap and learned to takeit for granted. But our water supply systems show increasing signs ofstrain. Rivers, lakes, ponds, streams, and other sources of surfacewater depend on rainfall, and regions involving twenty-eight states wereparched by drought in the spring of 1981. New York City declared adrought emergency on Jan. 19, 1981, enacting water restrictions thatlasted several months. The city of West Palm Beach rationed drinkingwater in May of 1981.

Many regions of our country have enjoyed a steady supply of water fromvast underground reservoirs called aquifers. The Ogallala aquifer,spanning 800 miles (1280 kilometers), supplies drinking water tocommunities from West Texas to South Dakota and provides irrigationwater for a major agricultural region. Aquifers accumulate overeons--only a tiny fraction of our rainfall seeps into them. In someparts of the American southwest people are drinking groundwater thatfell as rain ten thousand years ago.

We're pumping water out of our aquifers a billion gallons a day fasterthan rainwater is seeping into them. We're mining a precious resource,and in many places the lode is running dry. In California's San JoaquinValley an area the size of Connecticut has sunk as much as 30 feet (9.1meters) in the last twenty-five years because of excessive groundwaterremoval. Overuse of groundwater threatens the existence of midwesternagriculture. "It varies, depending on where you are, but there are somepeople projecting that as early as the year 2000 there will be parts ofNebraska with their water supplies so depleted that farming may neverreturn" according to Michael Jess, Nebraska water planner (Newsweek,2/23/81). In May 1981 in Winter Park, Florida the earth caved in,swallowing part of the city and creating a circular chasm 400 feet (121meters) wide and 100 feet (30 meters) deep. Underground limestonecaverns collapsed to create this huge sinkhole. When too much water wasremoved the limestone became brittle and crumbled.

Water supply in American coastal cities

Our major coastal cities, like inland areas, rely on fresh water.Purification of ocean water is rarely attempted. New York City drawswater from reservoirs in the Catskill Mountains 125 miles (200kilometers) to the northwest, then delivers this water to citizens witha highly centralized distribution system. Within the city all the waterfor eight million people rushes through two immense undergroundwaterways known as City Tunnel #1 and City Tunnel #2. Built in 1917 and1936, these tunnels have operated continuously ever since. They lie asfar as 800 feet (243 meters) below the ground and provide no access formaintenance or inspection. Maurice Feldman, a former New York City watercommissioner, has predicted that the tunnels will collapse within ten toforty years. In 1970 the city began digging a third tunnel 60 miles (96km) long and 24 feet (7 meters) in diameter, blasted out of solid rockand lined with concrete. New York City's financial crisis interruptedconstruction in 1975. At that time the Army Corps of Engineers estimatedthat the city water pipes were leaking 100,000,000 gallons(4,400,000,000 liters) a day, the rate of water consumption in SanFrancisco. Construction resumed in 1977. Current estimates of the totalcost of building City Tunnel #3 range from five to ten billion dollars.

Los Angeles, too, imports fresh water by mammoth feats of engineeringrather than purifying ocean water. Residents of Los Angeles rely on theOwens Valley 340 miles (544 km) to the north and the Colorado River 240miles (384 km) to the east. Removal of water from the Owens Valleycaused Mono Lake to drop 44 feet (13.4 m) since Los Angeles begandrawing water from its tributary streams in the 1920's. Until 1981 tensof thousands of migratory birds nested at Mono Lake and fed on brineshrimp from the lake's salty waters. But as the lake drained itssalinity increased, and it became too salty for brine shimp to survive.Without an adequate food source, virtually all the California Gullchicks hatched at Mono Lake in 1981 died. A recent congressional billthat would make Mono Lake a national park has jeopardized the flow ofwater from the Owens Valley to southern California.

Three fourths of the water used in Los Angeles and San Diego comes fromthe Colorado River. Nearly a third of the power generated by Hoover Damis used to pump Colorado River water through enormous canals, tunnels,and aqueducts to the deserts and coastlines of southern California. TheColorado is the only major source of surface water in thesouthwest--residents of Colorado, Utah, and Arizona also rely on it. In1985 the Central Arizona Project will begin transporting Colorado Riverwater eastward across three hundred miles of desert to Phoenix andTucson. California's allotment will diminish by about 20%, or 325billion gallons (1.4 trillion liters) per year. Southern Californiansmay face stringent water conservation measures unless they can findanother source of water.

Water Pollution

Problems of water scarcity are intensified by pollution of our freshwater supplies. Trihalomethane gases, known to cause cancer inlaboratory animals, contaminate virtually all our drinking water as aresult of the chlorination process city water systems use to prevent thespread of waterborne diseases. Trihalomethanes form when chlorineinteracts with algae, microorganisms or other organic materials in thewater. Other contaminants originate in the delivery system--lead andasbestos from water pipes leach into our tapwater.

Pollutants are also contaminating groundwater. Salt thrown on icyroadways has worked its way into aquifers in New England--residents ofseveral Massachusetts communities receive notes with their water billswarning them that the sodium content of their tapwater is dangerouslyhigh and advising them to drink bottled water. More than 600 wells inthe New York City area have been closed during the past three years dueto chemical contamination. Wells providing half the drinking water forresidents of Atlantic City, New Jersey are in imminent danger ofcontamination by a huge plume of toxic chemicals dumped over a decadeago. In California's San Joaquin Valley, where 80% of the people rely onwells for drinking water, many wells are being shut down because theycontain a highly toxic pesticide known as DBCP (dibromochloropropane).Agricultural pesticides and industrial solvents such astrichloroethylene, dioxane, and benzene had entered groundwater in atleast 250 sites as of September 1980, according to a report by the HouseGovernment Operations subcommittee. There are more than 50,000 hazardouswaste dumps in the United States--no one knows how many of them areleaking toxic chemicals into our water supplies. Once groundwater iscontaminated it's likely to stay contaminated for hundreds, eventhousands of years.

Water Distillation

For thousands of years people have respected distillation as a perfectseparation technique for purifying water. Distillation involves boilingthe water, moving its vapors to a different location, and condensing thevapors to obtain pure water. Aristotle (384 B.C.) mentions theevaporation of salt water to obtain fresh water. Alexander ofAphrodisias (circa 100 B.C.) tells of sailors boiling seawater andhanging sponges in the steam to collect pure water for drinking. Theindividual water vapor molecules rising from the boiling seawater haveno way to carry off the salt--the steam is pure water vapor. The mainproblem with distillation is the extremely high amount of energy ittakes to boil water.

Home water stills

Some people purify their tapwater with a home distillation apparatusknown as a still. Conventional tapwater stills consist of a boilingchamber, a condensing chamber, and an electric heater. The heater boilsthe impure water. Steam travels to the condensing chamber and condenses,becoming distrilled water. These stills remove any solid pollutants thatcontaminate our drinking water: asbestos or lead from decomposing waterpipes, salt thrown on icy roadways, arsenic or cadmium from industrialwastewater. But most tapwater stills won't remove toxic gases orliquids--these bubble off with the steam and contaminate the productwater.

The cost of operating tapwater stills limits their usefulness. Theydon't recycle energy. The electric heater has to supply all the energyfor heating and boiling the water--2.8 kilowatt hours per gallon. At 11cents per kilowatt hour, energy for distillation costs thirty-one centsper gallon (seven cents per liter). Most home stills can purify tengallons (44 liters) of water a day, enough for drinking and cooking fora small family. The energy to distill that much water costs $92.00 permonth. It would be advantageous to purify 200 gallons (880 liters) ofwater a day for bathing, showering, washing clothes, and washing dishes.But conventional stills with such a large output are huge and expensive,and the energy to run them costs over $1800 a month.

Conventional seawater stills

The abandoned desalting plant in Fountain Valley, California exemplifiesthe American experience with seawater purification. Built in 1975 at acost of $14 million, the plant was designed to distill fifteen milliongallons (66 million liters) of pure water per day, operating around theclock. But neighbors complained that the noise from its boilers wasintolerable and succeeded in shutting the plant down at night. The plantproduced only three million gallons (13 million liters) per day butconsumed all the energy its designers expected it would need for thefull fifteen million. After nine months of operation the governmentdecided the plant was too expensive to operate and shut it down. Todaypigeons roost there, using its insulation to build nests along thecatwalks. Similar stills in Chula Vista, California and Freeport, Texaswere sold for scrap.

Vapor compression distillation

Some large-scale seawater stills reduce the cost of distillation byrecycling energy. One energy-recycling process is known as vaporcompression distillation (Holden, U.S. Pat. No. 3,423,293). The goal ofthis process is to boil the seawater with heat given by the steam whenit condenses. (When the steam condenses it returns all the heat thatwent into boiling it off.) To recycle this heat, vapor compressionstills compress the steam so it will condense in metal tubes whichcontact the boiling seawater. The heat released by the condensing steamflows through the tube walls into the boiling seawater to generate moresteam. The condensed steam, now distilled liquid water, passes through acounterflow heat exchanger to heat up the incoming seawater.

By recycling energy this way vapor compression stills reduce the energyrequirements for distilling a thousand gallons (4.4 thousand liters) ofseawater from 2800 kilowatt hours to 75 kilowatt hours, lowering thecost from $196 to $5.25 (assuming industrial rates of 7 cents per kwh).From an enginering standpoint that's a remarkable accomplishment. Butfrom a practical standpoint it's still too expensive. If Los Angelesused conventional vapor compression stills to purify enough PacificOcean water to replace the Colorado River water it will lose to Arizonain 1985, the cost of energy alone would come to $5 billion in just threeyears.

People resort to seawater distillation only in extreme circumstances.Kuwait, an Arab nation rich in oil revenues but virtually devoid offresh water, relies almost entirely on desalted water. All the desaltingplants in the world produce a total of a billion gallons (4.4 billionliters) of pure water a day, approximately the rate of water use bypeople in the Los Angeles basin.

Reasons for the inefficiency of vapor compression stills

Vapor compression stills are inefficient because the tubes whichtransfer heat from the condensing steam into the boiling seawater don'thave enough surface area. Many factors limit the available surface area.Tubes are expensive to build and expensive to buy. They usually must bewelded along one seam and at both ends. It's impractical to pack thetubes too densely because all the tubes must be accessible for periodiccleaning, and tubes welded in the center of complicated tube bundles aredifficult to clean. With a limited area for condensing, the steam hastended to condense slowly.

The only way to condense the steam faster with limited surface area hasbeen to compress it substantially--and high compression creates amultitude of problems. Most important, high compression requiressubstantial energy. High compression demands bigger, more expensive,less efficient compressors and thicker, more heat resistant tubes.Compressing the steam substantially makes the tubes much hotter than theseawater, creating a violent boiling action that wastes energy inturbulent motion of the water. A vapor barrier forms on the hot tubesand interferes with their ability to transfer heat into the water. Allthese factors reduce efficiency in conventional vapor compressionstills.

Similar problems plague the counterflow heat exchange process whichthese systems use to heat up the cold seawater. To prevent heatexchangers from being massive and expensive the universal designstrategy has been to move heat through a small area by forcing theliquids through their channels under high velocities and high pressuresand by agitating the liquids to create a turbulent flow pattern. Thisapproach presents many problems. High velocities and high pressuresrequire a lot of energy. High pressures demand that the metal wallstransferring heat be relatively thick to withstand the stress. Thethicker the walls, the more they resist the flow of heat. The turbulenceof the water dissipates energy. These factors reduce efficiency andincrease the cost of the process.

The high operating cost of conventional seawater stills reflects theirinefficiency. Scientists have long known of the theoretical possibilityof a more efficient process. Weinberg wrote in the Bulletin of theAtomic Scientists (26, 6, 69, 1970): "Theoretically, about 3 kilowatthours of work are required to separate the 300 pounds of salt which arecontained in 1000 gallons of seawater. If energy is available at, say,five mills per kilowatt hour, then the thermodynamic minimum cost ofdesalinating seawater would be 1.5 cents per thousand gallons. Of coursethis minimum can never be attained." In other words, the work whichcosts $5.25 with conventional vapor compression stills can theoreticallybe done for twenty-one cents at today's industrial rates of seven centsper kilowatt hour. The other $5.04 derives mainly from the inefficiencyof the stills.

The inefficiency of conventional seawater stills is the main reason whyocean water is essentially unavailable for human life support. In thedrought year of 1981 not one sizable American metropolitan area purifiedseawater for drinking. Not one acre of American farmland is irrigatedwith purified seawater. Distilling seawater requires too much energy.

Energy Supplies Global energy supplies

Every day the sun showers the earth with 400 trillion kilowatt hours ofsolar heat, 25,000 times more energy than people consume as fuel andelectricity. Instead of deriving fuel and electricity from this dailyincome of solar energy, we rely on our planetary savings account offossil fuels--petroleum, coal, and natural gas. These fuels formed asplants collected solar energy, stored it as chemical energy, then layinside the earth under high pressures for millions of years. Much of thepetroleum has already been burned. The remainder can last only a fewmore decades at current rates of consumption.

Basing our world energy system on fossil fuels creates many immediateproblems. The price of oil has skyrocketed from $1.50 a barrel in the1960's to $32.00 today. The United States pays a billion dollars a weekfor imported oil. Countries such as Chad, Ethiopia, Nepal, Burma,Burundi, Upper Volta, and India, having a per capita gross nationalproduct of less than $200, can't afford oil and are blocked in theirefforts to achieve a higher standard of living by a shortage of energy.Mining the fossil fuels is hazardous--deep mining of coal impairs humanhealth, strip mining of coal disfigures the environment, oil spillsdestroy marine life. Burning fossil fuels causes contamination of theearth's atmosphere.

Power generation

In the United States we produce 90% of our electricity in power stationswhich burn fossil fuels. These power stations consist of three mainelements: a boiler, a condenser, and a turbine. The burning fuel boilswater to generate a head of steam. As the steam expands from the boilerto the condenser it spins turbine blades. Electrical generators convertthe rotary motion of the turbines into electricity.

These power stations are fraught with many difficulties apart from theirdependence on expensive fuel supplies. They are enormouslyinefficient--they discharge more energy into the environment as wasteheat than they convert into electricity. A conventional coal-fired plantburns 500,000 pounds (226,500 kilograms) of coal per hour to produce1,000 megawatts of electricity (enough to supply a million people) and1,300 megawatts of waste heat. Furthermore, a coal-fired plant this sizedischarges 28,000 pounds (12,684 kilograms) of pollutants per hour intothe atmosphere. Acid rain caused by pollutants from midwestern powerplants has killed all the fish in more than two hundred lakes in theAdirondack Mountains of New York, once a favorite resort area.

Nuclear power stations

Nuclear power plants now supply 4-5% of our nation's electricity. Likepower plants fired by coal or petroleum, nuclear power stations boilwater to generate steam for spinning the blades of a turbine. Severalfactors limit the viability of nuclear power. One by-product of nuclearpower plants is plutonium, a man-made element 20,000 times morepoisonous than cobra venom. Plutonium must be stored for hundreds ofthousands of years before humans can handle it safely. Someone with 20pounds (9 kilograms) of plutonium could make an atomic bomb withinformation from unclassified publications. Another factor weighingagainst nuclear power plants is the phenomenal cost of building them. InFebruary 1982 two nuclear plants under construction near Satsop,Washington were scrapped. They were going to cost at least $23billion--four times the cost their buyers expected when constructionbegan. In 1980 sixty-nine nuclear construction projects were delayed andsixteen others cancelled in the United States, most of them victimizedby high costs and steep interest rates.

Fuel alcohol

Alcohol is an ideal universal fuel, appropriate for poweringautomobiles, heating buildings, or any other process now burningpetroleum, coal or natural gas. Alcohol fuel is solar energy, collectedand transformed into chemical energy by plants. Plants use the energy ofsunlight to build large sugar molecules from carbon dioxide and water.When the plants ferment under proper conditions the sugar breaks downinto carbon dioxide and alcohol. When the alcohol burns, energy isreleased.

Alcohol has received widespread appreciation as a high-grade motor fuel.When Otto invented internal combustion engines in Germany in thenineteenth century his prototypes burned alcohol. Henry Ford advocatedthe use of "power alcohol" to stimulate agriculture and capitalize on arenewable resource--he equipped his Model T's and some later cars withadjustable carburetors to accommodate either alcohol or gasoline. BeforeWorld War II forty countries were blending alcohol into gasoline.Detroit built cars for the Phillipines and New Zealand that ran onstraight alcohol.

Gasoline became the conventional motor fuel because it was readilyavailable at low cost. But as petroleum becomes scarce and expensivemore countries are turning to alcohol distilled from farm commodities asa fuel for motor vehicles. Brazil has begun a major program to eliminateoil imports entirely by running all its cars and industries on alcoholdistilled from home-grown sugar cane and manioc. (Manioc is a starchyplant whose roots are a valuable food product. It is the source oftapioca.) Governments of New Zealand, Australia, South Africa, Thailand,Kenya, the Sudan, the Dominican Republic, Guyana, and Jamaica areconsidering large-scale alcohol fuel production.

Science magazine (1979, Volume 195) and many other sources indicate thatalcohol delivers more power and better mileage than gasoline whileburning cooler and quieter. Most cars can run on alcohol with only minoradjustments to their carburetors. A professional race car driver, BobbyUnser, testified before Congress recently that he has burned alcohol inhis race cars for years and that he finds it "a lot safer, a lot nicerto work with than gasoline." Alcohol is safer because it doesn't burnexplosively at normal atmospheric pressure. If spilled in the oceanalcohol has no toxic effects. Alcohol burns clean--converting allAmerican automobiles to alcohol would reduce air pollution in thiscountry by 90%, according to Stanford Research Institute (now SRIInternational). The waste products of engines burning alcohol are carbondioxide and water vapor. These are also waste products of human beings.Engines burning alcohol in a closed room won't asphyxiate people.

Some writers have expressed concern that emissions from engines burningalcohol will cause a dangerous buildup of carbon dioxide in theatmosphere. Actually, alcohol-burning engines release the same amount ofcarbon dioxide the plants absorbed from the atmosphere to build thesugar molecules that produced the alcohol. In this sense, automobilesburning alcohol maintain a harmonious balance with nature.

Alcohol is as renewable as sunlight, and people can produce it almostanywhere. In a September 1980 report entitled "Alcohol from Biomass inthe Developing Countries" the World Bank offered the opinion thatalcohol is the main renewable energy source developing countries canproduce from their own resources. The World Bank expressed interest inhelping to design national alcohol programs.

Alcohol Distillation

Fuel alcohol must be distilled because when plants ferment they yieldonly 5% to 15% alcohol--the rest is water. Fuel mixtures require atleast 75% alcohol. Since alcohol evaporates more readily than water, thetwo can be separated by distillation. Alcohol producers have borrowedintact the stills of the beverage industry, consisting of metal columns30 to 60 feet (9 to 18 meters) high filled with packing material.Alcohol and water vapors condense and re-evaporate many times on thepacking material as they rise through the column. The vapors becomericher in alcohol as they reach the top.

The widespread use of alcohol fuel is restricted by the energyrequirements of distillation. Column stills require approximately 45,000British Thermal Units (12.6 kwh) of energy to distill one gallon (4.4liters) of 100% alcohol fuel. A gallon of alcohol has a fuel value of84,000 BTU (24.6 kwh). Burned in a 15% efficient internal combustionengine, it can accomplish only 14,000 BTU (4.1 kwh) of useful work. Ittakes more energy to distill alcohol than you can get back when you burnit. That's why alcohol is known as an "energy loser."

Column stills were designed for distilling alcoholic beverages in theearly nineteenth century when energy was cheap and whiskey wasexpensive. They require too much energy to produce fuel economicallytoday. The main source of their inefficiency is this: after thedistilled alcohol vapors leave the top of the columns, the heat theyyield in condensation doesn't get recycled. This heat is lost to theprocess. All the heat for boiling comes instead from steam produced inboilers fired by petroleum, coal, or natural gas.

Fuel Alcohol U.S.A., a monthly magazine devoted to the alcohol fuelindustry, reported in February 1982 that 160 proof alcohol (80% alcohol,20% water) is an excellent automotive fuel, superior in performance andeconomy to straight alcohol. Distilling 160 proof alcohol fuel requiresonly half as much energy as distilling straight alcohol. Even so, it'snot clear that alcohol fuel production can be economical.

Distillation has earned a reputation as a problematic technology,capable of making many contributions to human society but tooenergy-intensive to realize its potential value.

SUMMARY OF THE INVENTION

The invention distills liquids with little energy because it recyclesenergy efficiently. In essence this invention is a heat transfertechnology. It recycles energy to reduce the costs of many domestic andindustrial processes. The key to its efficiency is transferring heatover an extensive surface area. This section briefly describes the mainembodiment of the invention, discusses various applications, andexplains how the invention solves the problems discussed in thebackground.

Brief Description of the Main Embodiment The distillation process

Distillation is a process of evaporation and condensation. The feedliquid enters a boiling chamber, where part of it boils off. Vaporstravel to a condensing chamber and condense, becoming the product, orthe distilled liquid. The part of the feed liquid that doesn't boil offbecomes concentrated. This concentrated liquid, known as the blowdown,carries impurities out of the boiler. The invention recycles energy attwo points: first to heat the cold feed liquid to its boiling point,then to boil it.

In water distillation about 1200 BTU per gallon (1.5 kwh per liter) arerequired to heat the feed water from 60° F. (16° C.) to 212° F. (100°C.), its boiling point. The product and the blowdown give off the sameamount of energy, 1200 BTU per gallon (1.5 kwh per liter), when theycool from 212° F. to 60° F. (from 100° C. to 16° C.). The inventiontransfers heat from the product and the blowdown into the feed water.

After the feed water reaches its boiling point, about 8000 BTU (2.3 kwh)of heat energy are required to convert a gallon of it to steam. Thesteam gives back 8000 BTU (2.3 kwh) when it condenses. The inventiontransfers heat from the condensing steam into the boiling water.

The hardware

A counterflow heat exchanger transfers energy from the hot product andthe hot blowdown into the cold feed liquid. The counterflow heatexchanger is built by stacking thin sheets of stainless steel withgaskets to form channels for the liquids. Every sheet transfers heatfrom hot liquid flowing in one direction on one side into cold liquidflowing in the opposite direction on the other side.

A boiler-condenser unit called a core transfers energy from thecondensing vapors into the boiling liquid. The core is built by stackingthin sheets of stainless steel with gaskets to form an alternatingsequence of boiling chambers and condensing chambers. Heat fromcondensing vapors flows through the sheets to boil the liquid on theother side.

A compressor raises the pressure of the vapors so they will condense andgive up their energy. The work of the compressor yields amultiplier--the input energy for compressing the vapors allows you torecycle more than 100 times that much energy from the condensing vaporsback into the boiling liquid.

The design strategy

The design strategy of this invention is to transfer heat over anextensive surface area--at least two square feet for every gallon perhour of fluid passing through the system (0.8 square meters per literper hour). This strategy makes low-energy distillation possible for thefirst time. In water distillation the invention recycles more than 99%of the energy for heating and boiling the water. Less than 1% of thetotal energy for distillation must be added continuously from anexternal source. The next two paragraphs explain how extensive surfacearea leads to efficiency in the counterflow heat exchanger and the core.

Extensive surface area and gentle liquid flow in the counterflow heatexchanger

When the liquids communicate over an extensive area, they exchange heatreadily even when they flow gently--with low velocities, low pressures,and a laminar or regular flow pattern. Passing the liquids through theirchannels gently is a novel procedure offering many advantages. First,the liquids require little input energy to move through their channels.Since the liquids place little stress on the heat transfer sheets, thesheets may be very thin. Thinner sheets conduct heat better, containless material, weigh less, and cost less, and fewer of them are neededfor a given rate of heat transfer. The gentle movement of the liquidsdissipates little energy in turbulence, and also allows the heattransfer sheets to be stacked very close together. Close spacing of thesheets places the hot liquids and the cold liquid in intimate contactfor optimal heat transfer. This gentle approach results in a compact,inexpensive, efficient counterflow heat exchanger. The energytransferred from the hot liquids to the cold liquid may be 800 timesgreater than the input energy required to move the liquids through theheat exchanger.

Extensive surface area and low compression in the core

When the condensing vapors are placed in heat exchange relationship withthe boiling liquid over a large area, the vapors condense readily with avery small compression step. Compressing the vapors a minimal amount isa novel approach to distillation offering many advantages. Little energyis required to compress the vapors. Since the compressed vapors exertlittle force on the heat transfer sheets, the sheets may be very thin.Low compression also makes it possible to stack the sheets very closetogether for efficient heat transfer. In addition, standard inexpensivecompressors of simple construction may be used. The cumulative effect ofthis strategy is a compact, inexpensive, efficient boiler/condenserunit. The energy transferred from the condensing vapors to the boilingliquid may be 100 times greater than the input energy required tocompress the vapors.

Manufacturing techniques

This invention is relatively easy to manufacture. The basic constructiontechnique is simply stacking sheets of metal with gaskets and thenbolting them together. The modular design of the invention makes itappropriate for any scale--many sheets form a large unit, a few sheetsform a small one. The heat transfer sheets are so thin they may beconstructed from materials which are not particularly heat conductivesuch as glass or plastic, both of which are plentiful and inexpensive.

Maintenance

The owner can perform all routine maintenance of the invention withcommon tools. To gain access to the heat transfer sheets for periodiccleaning one simply removes the bolts which hold them together.

Applications of the Invention

In some applications of this technology the object of the boiling andcondensing process is to collect the substance that boils off. This istrue, for example, in purifying water and distilling alcohol. In someother applications the object is to collect the part that doesn't boiloff. This is true in drying grains, drying clothing, and concentratingor dehydrating solutions. In a third type of application, the inventionuses steam to generate electrical power, a novel capability for adistillation apparatus. In all these situations the invention recyclesheat efficiently. The remainder of this section will discuss some of itsapplications.

Water purification

A device slightly larger than a microwave oven will purify 15 gallons(66 liters) of tapwater per hour while drawing less than 1 kilowatt ofpower. It removes all pollutants--solids, liquids, or gases. Its energycosts for distilling ten gallons (44 liters) per day come to less than$3 a month (at 11 cents per kilowatt hour). With this invention theenergy to purify two hundred gallons (880 liters) of water a day wouldcost only $44 a month. The invention also makes it economically feasibleto purify and recycle household wastewater during droughts or in areasof fresh water scarcity.

Larger units will enable municipal water districts to remove toxicchemicals from drinking water supplies. This invention will purify athousand gallons (4.4 thousand liters) of fresh water while drawing onlytwo kilowatt hours of energy, at a cost of 14 cents (assuming industrialrates of 7 cents per kwh). The invention will also prevent the formationof trihalomethane gases by removing the organic materials in the waterbefore chlorine is added. After the water has been distilled, only traceamounts of chlorine will be needed to keep it pure.

Many industries will value this invention because it can extract toxicchemicals inexpensively from their wastewater, so both the chemicals andthe water can be recycled. In industrialized countries water recyclingwill significantly reduce environmental pollution. In developingcountries the ability to recycle water inexpensively will facilitateindustrial development, since industries will not be dependent on vastwater resources.

The invention also gives inexpensive access to pure water from theoceans. In large-scale settings this invention will purify a thousandgallons (4.4 thousand liters) of ocean water for 6 kilowatt hours, theamount of energy it takes to pump that much water from the ColoradoRiver to Los Angeles. The invention has the potential to make oceanwater available for drinking and irrigation on a large scale for thefirst time in human history. In the United States the pipelines whichcarry fresh water to our coastal cities could carry water in theopposite direction, from the oceans to the deserts and the Great Plains.Abundant pure water from the oceans will enable people to reclaimdeserts along 50,000 miles (80,000 kilometers) of coastline in theAmericas, Africa, Australia, and the Middle East.

Alcohol distillation

By recycling heat efficiently this invention reduces the energyrequirements of alcohol distillation by more than 90%. To distill agallon (4.4 liters) of 160 proof alcohol the invention requires only2000 BTU (0.6 kwh), about 5 cents' worth of energy. This newenergy-recycling distillation technology will make it possible foralmost any state or nation to become energy independent. The inventionis an ideal village-scale technology for the underdeveloped countries:ecologically sound, consistent with human dignity, easy to understandand repair, capable of operating with any source of rotary motion as anenergy input, and above all capable of producing premium liquid fuelfrom local materials at low cost. In coastal areas where feed stocks foralcohol are scarce, the ability of the invention to purify seawater forirrigation will make it easier to grow crops for energy production. Theinvention is much smaller than a conventional still--a unit the size ofa small refrigerator will enable many farmers to produce enough alcoholfrom their waste crops to run their machinery.

Dehydration and concentration

Many domestic and industrial processes are designed to remove water. Theinvention can reduce the cost of these processes up to 99% by recyclingenergy. For homeowners the invention will dry clothing, fruits, orvegetables. For the food processing industry it will concentrate fruitjuices, dehydrate food products, and dehydrate watery waste materials.Oil companies, who draw up huge quantities of brine when drilling foroil and pay to dispose of it, will value the invention's ability toseparate the salts from the water at low cost. The geothermal energyindustry will also welcome the ability to dehydrate brines inexpensivelyfor safe and easy disposal of salts and other minerals. Alcohol fuelproducers can use the invention to concentrate their fruit juices beforefermentation to obtain a higher yield of alcohol, and also to dry theirgrains and liquid residucs to sell them as animal feed.

Power generation

Like power plants fired by fossil fuels or nuclear energy, the inventiongenerates electricity by boiling water to create a head of steam. Theinvention is novel in that it recycles heat to sustain the boilingaction. The power generation process requires a flow of fresh water intothe boiling chambers and a flow of concentrated brine into thecondensing chambers. Energy becomes available because of the differencein steam pressure between the fresh water and the brine. The freshwater, having a higher steam pressure, evaporates easily. The brine,having a lower steam pressure, evaporates with more difficulty. Steamnaturally flows from the high pressure area (the boiling fresh water) tothe low pressure area (the hot brine). The flowing steam spins theblades of a turbine placed in its path, and an electrical generatorlinked to the turbine transforms the rotary motion into electricity.When the steam reaches the hot brine it condenses and gives up its heat.This heat flows through stainless steel sheets back into the fresh wateron the other side to sustain the boiling.

Any fresh water mixed into saturated brine by a power still cantheoretically generate as much power as it would from a dam nearly threemiles (4.8 kilometers) high. Hoover Dam, by comparison, is 726 feet (221meters) high. In practical applications every gallon of fresh water apower still mixes into saturated brine can generate 50 watt hours ofelectrical power (11 watt hours per liter). Wherever fresh water andbrine exist naturally this process may prove very valuable. The riverwater and household wastewater running into the Great Sale Lakerepresent a substantial untapped energy source. The Israelis alreadyhave plans to pump ocean water from the Mediterranean Sea to the DeadSea just to keep the Dead Sea from drying up. Since the Dead Sea wateris twenty times saltier than the Mediterranean Sea water, power stillscould generate electrical power by mixing the two. In this process nofuel is burned, virtually no waste heat is released, and there is noenvironmental pollution.

The table on the following page compares the energy requirements of thisinvention with those of conventional equipment. Comparative costs arealso listed. The cost figures assume a rate of 11 cents per kilowatthour for every process except large-scale seawater distillation. Thecosts of large-scale seawater distillation are figured at industrialrates of 7 cents per kilowatt hour. The remainder of this documentdescribes in detail the new heat exchange technology which makes thesecost breakthroughs possible.

    ______________________________________                                        TABLE OF COMPARATIVE ENERGY                                                   REQUIREMENTS AND COSTS                                                                     Convential     This                                                           Stills         Invention                                         ______________________________________                                        Tapwater     2800 watt hours                                                                              50 watt hours                                     Distillation ($.31) per gal.                                                                              ($.006) per gal. - 636 watt hours 11 watt                                     hours                                                          ($.08) per liter                                                                             ($.001) per liter                                 Small-Scale  2800 watt hours                                                                              60 watt hours                                     Seawater Distillation                                                                      ($.31) per gal.                                                                              ($.007) per gal.                                               636 watt hours 13 watt hours                                                  ($.08) per liter                                                                             ($.001) per liter                                 Large-Scale  75 kwh ($5.25) 6 kwh ($0.42)                                     Seawater Distillation                                                                      per 1000 gal.  per 1000 gal.                                                  19 kwh ($1.33) 1.4 kwh ($0.10)                                                per 1000 liters                                                                              per 1000 liters                                   Alcohol Fuel 25,000-45,000 BTU                                                                            2,000 BTU                                         Distillation ($.81-$1.45) per gal.                                                                        ($.06) per gal.                                                1.7- 3.0 kwh   0.13 kwh                                                       ($.18-$.33)    ($.01) per liter                                               per liter                                                        ______________________________________                                    

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a stacked-sheet core and heat exchanger.

FIG. 2 is an exploded drawing of the core of FIG. 1.

FIG. 3 is an exploded drawing of a variation of the core of FIG. 1.

FIG. 4 is an exploded drawing of the heat exchanger of FIG. 1.

FIG. 5 is an isometric view, partially exploded and partially insection, of a spiral core and heat exchanger.

FIG. 6 is an isometric view, partially in section, of a batchdehydrator-concentrator.

FIG. 7 is a cross-section of the boiling chamber of FIG. 6 along lines7--7.

FIG. 8 is a cross-section of the condensing chamber of FIG. 6 alonglines 8--8.

FIG. 9 is an isometric view, partially exploded, of a batch dehydrator.

FIG. 10 is a cross-sectional end view of the batch dehydrator of FIG. 9.

FIG. 11 is a cross-sectional side view of the batch dehydrator of FIG.9.

FIG. 12 is an exploded drawing of a power generator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This section describes the various embodiments of the invention andtheir applications: water purification, counterflow heat exchange,alcohol distillation, dehydration and concentration of liquids, dryingof solids, and generation of electrical power. In each application theinvention recycles energy efficiently. In essence, every embodiment ofthe invention is a heat exchange apparatus, and every process describedis a method of heat exchange.

Water Purification

The method is distillation: boiling water to convert it to pure steam.When the steam condenses it becomes pure liquid water. The inventionrecycles energy in two ways. First a counterflow heat exchanger heatsthe feed liquid nearly to its boiling point with energy given by theproduct and the blowdown. Then a boiler-condenser unit called a coreboils the feed liquid with energy given by the condensing steam.

The stacked-sheet still

FIG. 1 shows a stacked-sheet heat exchanger (11) and core (12) forpurifying or concentrating liquids. Both the heat exchanger (11) and thecore (12) are built by stacking sheets of metal, or some other material,with gaskets.

The counterflow heat exchanger.

The counterflow heat exchanger (11) is built from 100 sheets ofstainless steel type 316, known for its ability to resist corrosion fromseawater. Each sheet measures 9"×12" by 0.01" (23 cm×30 cm×0.25 mm).Silicon rubber gaskets maintain a separation of 0.032" (0.81 mm) betweenthe sheets. Fiberglass end plates stabilize the heat exchanger. Thefront end plate (13) measures 9"×12"×0.25" (64 cm× 30 cm×6.35 mm), andthe rear end plate (14) measures 11"×12"×0.25" (27.9 cm×30 cm×6.35 mm).

In the heat exchanger (11) the areas between the sheets form chambersfor liquid flow. Chambers for hot liquid (the product or the blowdown)alternate with chambers for cold liquid (the feed water). Every sheettransfers heat from hot liquid flowing in one direction on one side intocold liquid flowing in the other direction on the other side.

The core.

The core (12) is built from 51 sheets of stainless steel type 316. Eachsheet is 16"tall, 12" wide, and 0.01" thick (41 cm×30 cm×0.25 mm). Oneside of each sheet serves as a boiling surface, and the other sideserves as a condensing surface. Silicone rubber gaskets keep the sheets0.06" (1.52 mm) apart. Two fiberglass end plates stabilize the core--thefront end plate (17) measures 16"×12"×0.25" (41 cm×30 cm×6.35 mm), andthe rear end plate (18) measures 16"×14"×0.25" (41 cm×36 cm×6.35 mm).

In the core (12) the areas between the sheets serve as chambers forboiling and condensing. All the boiling chambers interconnect and formthe boiler; all the condensing chambers interconnect and form thecondenser. Boiling chambers and condensing chambers alternate. Everysheet transfers heat from steam condensing on one side into a liquidboiling on the other.

The peripheral equipment.

A compressor (16) bolted onto the core (12) blows vapors from theboiling chambers to the condensing chambers. (One example of a suitablecompressor is Lamb compressor #115962.)

Three hoses in FIG. 1 connect the core (12) to the heat exchanger (11).The hose on the right (19) carries the blowdown from the core (12) tothe heat exchanger (11). The hose in the center (21) carries the productfrom the core (12) to the heat exchanger (11). The hose on the left (22)carries feed liquid from the heat exchanger (11) to the core (12). Thishose (22) contains a gas-liquid separator (28) for removing dissolvedgases and liquids from the feed liquid. Dissolved gases and liquids comeout of solution and leave through the gas-vapor outlet (35). (Thisprocess will be explained in more detail in a later section.)

The same hose (22) also contains a supplemental heater (23) whichprovides energy for start-up, then operates intermittently to maintainthe desired operating conditions. (One example of a suitable heater isthe "Immersion Heater" manufactured by A. O. Smith Co.) The heater (23)is controlled by a pressure switch (24) sensitive to steam pressure inthe boiler. This pressure switch (24) connects to the boiler through ahose (26) which penetrates an opening (27) in the end plate (17). Whenthe pressure in the boiler raises more than 1 p.s.i. (0.07 kilograms persquare meter) above ambient pressure the switch (24) opens and shuts offpower to the heater (23). When the pressure in the boiler becomes lessthan 0.5 p.s.i. (0.035 kg/sq m) above ambient pressure the switch (24)closes, and the flow of power to the heater resumes. The switchmanufactured by Henry G. Dietz Co. (#171D8WC) gives acceptable results.

An alternative way to control the heater would be to monitor thetemperature of the water in the boiler. In this event a thermistor wouldreplace the pressure switch. Thermistor AP1H104-6 manufactured byMidwest Components Inc. would serve adequately. The thermistor wouldshut off power to the heater (23) when the water temperature reached213° F. (101° C.) and restore power to the heater (23) when the watertemperature dropped to 212° F. (100° C.).

The three hoses near the lower left corner of the heat exchanger (11)convey liquids to and from the system--hose (25) is an inlet for thefeed liquid, hose (20) is an outlet for the product, and hose (15) is anoutlet for the blowdown.

The Relative Importance of the Specifications.

Of the structural dimensions specified for the core (12) and the heatexchanger (11) only two are critical: the thickness of the sheets andthe distance between them. The thickness of the sheets should be withinthe range of 0.001" to 0.02" (0.025 mm to 0.51 mm). It would be possibleto use sheets outside this range, but thinner sheets would easily tearor punctucre, and thicker sheets would reduce efficiency, besides beingprohibitively expensive. Sheets with a thickness of 0.01" (0.25 mm) aresturdy, inexpensive, and extremely heat conductive. The distance betweenthe sheets must be within the range of 0.005" to 1.0" (0.13 mm to 2.54cm) in the core (12) and within the range of 0.005" to 0.25" (0.13 mm to6.4 mm) in the counterflow heat exchanger (11). The counterflow heatexchanger (11) achieves optimal efficiency when the spacing between thesheets if 0.1" (2.54 mm) or less, a spacing of 0.032" (0.81 mm) beingideal for most purposes.

Other aspects of the hardware offer a broad range of choices. The sheetsmay be fabricated from stainless steel, aluminum, brass, copper-nickel90/10, glass, or polyester--any material which can be formed into a thinsheet and maintain its structural integrity at the operatingtemperatures. The height and width of the sheets are not particularlyimportant, except in subtle ways to be mentioned later. Many commongasket materials will serve for the gaskets. The dimensions andmaterials of the end plates are unimportant, so long as they provideenough stability. Virtually any vapor compressor will serve adequatelyif its flow rate matches the flow rates of the core and the heatexchanger.

The number of sheets in the core and in the counterflow heat exchangerdepends on the desired flow rate and efficiency. For a minimal flowrate, one heat transfer sheet is sufficient to create either a core or acounterflow heat exchanger. Combined with two end plates, one sheet willcreate the basic structure: a chamber containing relatively warm fluidon one side of the sheet and a chamber containing relatively cool fluidon the other side. The stacked-sheet core ordinarily comprises at leastfive sheets. The core (12) of FIG. 1, built from 51 sheets, purifies 15gallons (66 liters) of water per hour. The counterflow heat exchanger(11) of FIG. 1, containing 100 sheets, heats up 30 gallons (132 liters)of cold water per hour, drawing heat from 15 gallons (66 liters) ofproduct and 15 gallons (66 liters) of blowdown.

An Exploded Drawing of the Core.

FIG. 2 is an exploded drawing of the core (12) of FIG. 1 exposing twoheat transfer sheets (29 and 31). Both sheets have a gasket affixed toone surface. The sheet (29) on the left has a gasket (32) for a boilingchamber (33). The boiling chamber (33) lies between the two sheets, itsboundaries defined by reference numbers (51) at the top, (30) at thebottom, (41) on the left, and (60) on the right.

The sheet (31) on the right has a gasket (34) for a condensing chamber(36). The condensing chamber (36) lies between the heat transfer sheet(31) and the front end plate (17). (Within the stack, of course, thecondensing chambers lie between two adjacent heat transfer sheets--notbetween a sheet and an end plate.) The boundaries of the condensingchamber are indicated by reference numbers (52) at the top, (40) at thebottom, (39) on the left, and (80) on the right.

The Paths of Water and Steam through the Core of FIG. 2: The feed water.

A hose (22) carries the heated feed water into the core (12) through anopening (37) in the end plate (17). Then the feed water passes throughholes (38) 1" (2.54 cm) in diameter in all the sheets. It can't enterthe condensing chambers (36) because the gaskets form a barrier (39).But it passes into all the boiling chambers (33) through openings (41)in the gaskets (32). A seal (42) holds the water and steam inside thesystem. When the water touches the heat transfer sheets (29 and 31) itreceives heat from steam condensing in the adjacent chambers. The waterboils and steam rises.

The Steam.

The compressor (16) draws steam out of the boiling chambers (33) andblows it into the condensing chambers (36). The steam leaves the boilingchambers through holes (43) 1" (2.54 cm) in diameter near the top of allthe sheets. It flows through an opening (44) in the end plate (17) andan opening (46) in the compressor manifold (47). Then the compressor(16) compresses the steam and ejects it through a second compressormanifold (48) and through a hole (not shown) in the rear end plate (18).The compressed steam flows through holes (49) 1/2" (1.27 cm) in diameterin each sheet. It can't enter the boiling chambers (33) because thegasket (32) forms a barrier (51). But it enters every condensing chamber(36) through an intake manifold (52).

When the steam touches the heat transfer sheets it condenses and givesup its heat. The steam condenses at a temperature hotter than theboiling liquid as a result of its being compressed. The heat given bythe condensing steam flows from hot to cold--from the condensingsurface, through the sheet, into the boiling water.

The product.

The condensed steam, now distilled liquid water, drips down the sides ofthe sheets and flows out of the core. It leaves the condensing chambersthrough an outlet manifold (40). Then it flows through holes (53) 1/2inch (1.27 cm) in diameter at the bottom of each sheet. As the productleaves the core (12) a barrier (30) keeps it from entering the boilingchambers. The product exits through an opening (54) in the front endplate (17). A hose (21) carries it to the heat exchanger.

The blowdown.

The blowdown leaves the boiling chambers through openings (60) in thegasket. Then it passes through holes (56) 1" (2.54 cm) in diameter atthe side of every sheet. A barrier (80) prevents the blowdown fromentering the condensing chambers as it leaves the core. The blowdownpasses through an opening (57) in the front end plate (17), then entersan outlet hose (19). A spill tube (58) in this hose regulates the levelof water in the boiling chambers.

Other liquids may be distilled with this procedure. The operatingconditions will vary, depending on the boiling temperture of the liquid.

Other Details of FIG. 2.

A few details of the drawing remain to be mentioned. Small assemblyholes (59) are punched on the perimeter of all the sheets. There arealso four assembly holes (61) in the center of each sheet. In addition,the drawing shows assembly holes (50) in the end plates and assemblyholes (55) in the compressor manifold (47). Bolts (not shown) passthrough all these assembly holes to hold the system together. The smallsections of gasket on the boiling and condensing surfaces are spacers(62). They hold the sheets apart at any pressure from a complete vacuumto two atmospheres.

The core (12) and heat exchanger (11) are built by cutting stainlesssteel sheets to size, punching holes in them, stacking them withgaskets, and bolting them together.

Performance Characteristics of the Stacked-Sheet Core.

The stacked-sheet core (12) of FIGS. 1 and 2 purifies fifteen gallons ofwater per hour (66 liters/hour) while compressing the steam by 1 p.s.i.(0.07 kg/sq cm). Like the other embodiments of the invention, it yieldsa high energy multiplier--in other words, it recycles large quantitiesof energy in return for a small energy input. This core recycles 120,000BTU (35.2 kwh) of heat energy per hour (enough to boil off fifteengallons or 66 liters of water). The energy required to compress thesteam by 1 p.s.i. (0.07 kg/sq cm) is 163 watt hours, or 556 BTU. Theratio of the recycled energy to the input energy is 215 to 1.

The 163 watt hours of energy required for compressing the steam do notinclude losses due to inefficiency of the compressor and compressormotor. The Lamb compressor is approximately 50% efficient, and its motoris approximately 50% efficient. With this peripheral equipment 652actual watt hours are required to compress the steam. The ratio ofrecycled energy to input energy is slightly greater than 50 to 1.

There are several ways to increase the efficiency of the process. First,one could capture the waste heat from the compressor motor. Second, onecould use more efficient peripheral equipment: an 80% efficientcompressor driven by a 90% efficient electric motor. Third, one coulduse more sheets--doubling the heat transfer surface area will reduce byhalf the compression step required for a given output of distilledwater. Incorporating all these steps would reduce the total energyrequirements to 6.8 watts hours per gallon (1.5 watthours/liter)--raising the ratio of transferred energy to input energy to347 to 1.

Design Strategy in the Stacked-Sheet Still.

The basic design strategy for all embodiments of the invention is toprovide extensive heat transfer surface area for a given flow rate--atleast 2 square feet of heat transfer surface for every gallon per hour(0.8 sq m/liter/hour) of fluid passing through. (The "fluid passingthrough" refers to the distilled liquid in the cores and to the coolerliquid in the counterflow heat exchangers.) The core (12) of FIGS. 1 and2 establishes heat exchange relationship between the condensing steamand the boiling water over approximately 45 square feet (4.2 sq m) toboil off 15 gallons (66 liters) of water per hour--a ratio of 3 squarefeet per gallon per hour (1.2 sq m/liter/hour).

Sheet material is an ideal medium for transferring heat because itoffers extensive surface area at low cost. Compared to the metal tubesused in previous heat-recycling stills, sheet material provides at leasttwenty times the surface area for the same price.

Low Compression.

Extensive heat transfer surface area in the core makes it possible tocondense the steam readily while compressing it only a small amount,less than 2 p.s.i. (0.14 kg/sq cm). Several important advantages of alow compression step have already been mentioned: the low energyrequirements for compressing the steam, the opportunity to use thinsheets, the opportunity to stack the sheets close together for improvedheat transfer, and the opportunity to use simple, inexpensive,long-lasting, quiet, efficient compressors.

Another advantage of low compression is a low temperature differencebetween the sheets and the boiling liquid. When the steam is compressedby less than 2 p.s.i. (0.14 kg/sq cm) the boiling surface of the heattransfer sheets will remain less than 8° F. (4.4° C.) hotter than theboiling water. With less than 1 p.s.i. (0.07 kg/sq cm) of compressionthis temperature difference will not exceed 4° F. (2.2° C.). A smalltemperature difference is valuable for three reasons. First, the waterdoesn't dissipate energy in random, turbulent motion--it boils gently,staying mostly at rest. Second, the water stays in close contact withthe sheets. Virtually no steam barrier forms on the boiling surface toinsulate the water from its heat source. Third, the relatively lowtemperature of the sheets reduces the problem of scale. Scale, a crustformed by the impurities left behind when seawater evaporates, reducesheat flow and must be removed periodically. This invention has lessproblem with scale than any previous distillation technology because thesheets aren't hot enough to bake the impurities onto the metal. Most ofthe impurities simply wash out with the blowdown. All these advantagesderive directly from the extensive surface area-low compressionapproach.

Some minimum of compression is always necessary because steam must bepushed slightly "uphill," from a low pressure area in the boiler to ahigh pressure area in the condenser. The condenser has a higher pressurebecause the pure water there evaporates even more readily than theimpure water in the boiler, and so exerts a higher steam pressure. Tomove steam uphill from the boiler to the condenser and cause it tocondense, the compressor must supply a pressure step equal to thedifference in steam pressures, plus a little more. As the compressionstep becomes lower and approaches the difference in steam pressures, theenergy requirements of the process may approach the theoretical minimum.

In seawater distillation the difference in steam pressure between thedistilled water in the condenser and the salty water in the boiler isequal to seventeen inches (43 cm) of water pressure, or about 0.6 p.s.i.(0.042 kg/sq cm). The minimum compression step to cause condensation inseawater distillation, then, is some amount slightly greater than 0.6p.s.i. (0.042 kg/sq cm). The energy to provide this pressure differencecomes to approximately 6 kilowatt hours per thousand gallons--very near3 kilowatt hours, the theoretical minimum of energy required to distillseawater according to classical physics. This invention demonstrates anoperational method of distilling seawater with energy requirementsapproaching the theoretical minimum.

Fresh water distillation requires even less energy than seawaterdistillation. In fresh water distillation less compression is requiredto move steam uphill into the condenser because the difference in steampressure between the distilled water and the impure water is veryslight.

Other considerations for high efficiency in distillation

In order to recycle heat in distillation with efficiency approaching thetheoretical limits, it is also necessary to do the following things:

1. Distribute impurities evenly throughout the boiler.

Local concentrations of impurities will raise the boiling temperature ofthe water and may prevent it from boiling. The core of FIGS. 1 and 2removes impurities from all parts of the boiler continuously bymaintaining an even flow of water across the sheets in every boilingchamber.

2. Distribute heat evenly throughout the boiler.

For high efficiency the water must boil throughout its volume, not justat hot spots. The core of FIGS. 1 and 2 distributes heat evenly byspreading water evenly across the boiling surfaces and by spreadingsteam evenly across the condensing surfaces. It spreads water across theboiling surfaces by partially filling each boiling chamber with water,regulating the level so that when the water boils it covers the entireboiling surface. This method has one disadvantage: the pressure on thewater at the bottom of the boiler increases due to the weight of thewater above it. This pressure increase raises the boiling temperature ofthe water and can keep it from boiling. The effects of the pressureincrease are minimized by having a boiler only 1 foot (0.3 meters) deep.Even in large-scale applications the depth of the boiler in thisembodiment would not exceed 3 feet (0.9 meters). This core spreadsvapors evenly across the condensing surfaces with a rubber manifoldcontaining many small holes, the pressure drop across each hole beinggreat enough to ensure that steam enters each hole at an equal rate.

3. Minimize the pressure drop across the condenser from entrance toexit.

Any pressure drop across the condenser means that the compressor must doextra work just to push the steam through the condensing chambers. Inthe core of FIGS. 1 and 2 the condensing chambers are only 1 to 3 feet(0.3 to 0.9 meters) long, and so the pressure drop across them isminimal--less than 0.25 p.s.i. (0.018 kg/sq cm). Very little of thecompressor's energy is wasted in pushing the steam through the chambers.Most of the compressor's energy is used productively, for compressingand condensing the steam.

4. Remove non-condensible gases.

One example of a non-condensible gas is the air dissolved in seawater.When the seawater boils, the air comes out of solution and enters thecondenser along with the steam. But the air won't condense. If the airis allowed to accumulate in the condenser it will slow down thecondensation of the steam and reduce efficiency. The core of FIGS. 1 and2 exhausts non-condensible gases by maintaining a continuous flow ofsteam throughout the condenser and ensuring that some excess steam exitsthe condenser at all times to entrain the gases.

5. Remove the distilled water from the condensing chambers quickly andeasily.

This is important for two reasons. First, the distilled water interfereswith the flow of heat by insulating steam from the condensing surfaces.Second, the compressor's energy requirements increase if it has to blowthe distilled water out of the condenser. The core of FIGS. 1 and 2 hasvertical condensing surfaces only 1 foot (0.3 meters) high. Distilledwater drips down quickly and easily. The compressor does very littlework to push it out of the condensing chambers.

6. Keep the system in thermal balance.

This means adding or removing small amounts of heat to maintain thedesired operating conditions. The core of FIGS. 1 and 2 keeps itself inthermal balance by adding make-up heat intermittently, only whennecessary. To determine when make-up heat is needed one could monitoreither water temperature or steam pressure in the boiler. The core inFIGS. 1 and 2 monitors steam pressure and controls the heater with apressure switch in the manner described earlier.

7. Heat the feed liquid nearly to its boiling point before putting itinto the boiler.

If the feed liquid hasn't reached its boiling point when it enters theboiler, some of the energy given by the condensing steam must heat upthe feed liquid, and heat from an outside source must be added tosustain the boiling rate. The high efficiency of this invention dependsheavily on the ability of the counterflow heat exchanger to heat thefeed liquid to a temperature near its boiling point. The heat exchangerwill be examined in detail after a variation of the stacked-sheet coreis discussed.

A stacked-sheet core with a vertical-flow boiler

The core (65) of FIG. 3 is identical to the core of FIGS. 1 and 2 inmost respects. It is built from 51 sheets of stainless steel 0.01" (0.25mm) thick, spaced 0.06" (1.52 mm) apart. It purifies 15 gallons of waterper hour (66 liters/hr) with a compression step of 0.9 p.s.i. (0.06kg/sq cm). It provides approximatelly 3 square feet: (0.28 squaremeters) of heat transfer surface area for each gallon of distilled waterproduced per hour. It differs from the core of FIG. 2 only in the way itspreads liquids across the boiling surfaces. This core (65) introducesthe feed liquid at the top of each boiling chamber and allows it to dripdown the sides of the heat transfer sheets in a thin film. Thestructural changes required for the vertical-flow boiler are minor--oneextra hole (63) is punched in the sheets, and the gaskets (70 and 75)have a slightly different configuration.

The Paths of Fluids in the Vertical-Flow Boiler.

Fluids move through the core (65) of FIG. 3 just as they move throughthe core (12) of FIG. 2, except for the passage of feed liquid into theboiling chambers, which occurs in the following manner: First a hose(64) brings the feed liquid to the core (65). The feed liquid enters thecore (65) through an opening (66) in the front end plate. Then it flowsthrough a hole (63) 1/2" (1.27 cm) in diameter in all the sheets. Thefeed liquid can't enter the condensing chambers (67) because the gasketforms a barrier (68). But in each boiling chamber (69) the feed liquidenters an intake manifold (71) near the top of the sheet. It flowsthrough openings (72) in the intake manifold and cascades down the sidesof the sheets. The rest of the process occurs exactly as described inthe discussion of FIG. 2.

Advantages and Disadvantages of the Vertical-Flow Boiler.

The stacked sheet core (65) with the vertical-flow boiler offers twomain advantages. First, it recycles heat with slighly greater efficiencythan the horizontal-flow boiler shown in FIGS. 1 and 2 because pressureremains equal throughout the boiling chambers--there is no column ofwater to bear its own weight. As a result the water boils consistentlyin all parts of the chambers. Slightly less compression is required fora 15-gallon-per-hour (66 liters/hr) flow rate, and less make-up heat isneeded. The second advantage is closely related to the first: no matterhow deep the boiling chambers are, the water at the bottom of thechambers will boil readily. For this reason the vertical-flow boiler ismore suitable for large-scale units.

The main disadvantage of the vertical-flow boiler is the difficulty ingetting the water to flow evenly over the boiling surfaces. The watertends to flow in rivulets rather than an even film.

Having examined the stacked-sheet boiler-condenser units in detail, thisdiscussion will now explain how the same design principles are embodiedin the stacked-sheet counterflow heat exchanger.

The stacked-sheet heat exchanger

FIG. 4 is an exploded drawing of the heat exchanger (11) of FIG. 1exposing four sheets (73, 74, 76, and 77) of stainless steel. Each sheethas a gasket (78) attached to one surface. The gaskets (78) keep thesheets separated by 0.03 inches (0.76 mm) and also guide the paths ofthe liquids. The areas between the sheets serve as chambers (79, 81, 82,and 83) for liquid flow. Chambers for the incoming cold liquid alternatewith chambers for the outgoing hot liquids. The sheets transfer heatfrom the hot liquids flowing in one direction on one side into the coldliquid flowing in the opposite direction on the other side.

The six holes (84, 86, 87, 88, 89, and 91) at the left edge of thesheets, measuring 0.5 inches (1.27 cm) in diameter, allow liquids toenter and leave the heat exchanger. The smaller holes around theperiphery of the sheets are assembly holes (92) for bolts to hold theheat exchanger together.

The Paths of Liquids through the Stacked-Sheet Heat Exchanger: The feedliquid.

The feed liquid arrives at the heat exchanger through a hose (25). Itenters the heat exchanger through an opening (94) at the bottom of theend plate (13). Then it flows through the lowest hole (84) in everysheet. It can't get into the first chamber (79) because the gasket (78)forms a barrier (96). But the feed liquid enters the second chamber (81)and the fourth chamber (83) through openings (97 and 93) in the gaskets(78).

Within its chambers (81 and 83) the feed liquid flows back and forthacross the sheets along a path outlined by the gaskets, absorbing heatfrom the hot liquids in the adjacent chambers. After being heated thefeed liquid leaves its chambers through the uppermost hole (91) in thesheet. Then it flows through holes (91) in every sheet and through anopening (98) in the end plate (13). A hose (22) carries it to theboiler.

The product.

The product arrives at the heat exchanger from the condenser through ahose (21). It enters the heat exchanger through an opening (102) in theend plate (13). Then it flows through the second hole (89) from the topin every sheet. The product can't get into the first chamber (79) or thesecond chamber (81) because the gaskets (78) form barriers (101 and103). But the product enters the third chamber (82) and other chambersthrough openings (104) in the gaskets (78).

As the product flows through its chambers (82 and others) it gives heatto the feed liquid in the adjacent chambers (such as 81 and 83). Theproduct leaves its chambers through the second hole (86) from the bottomin every sheet. Then it passes through an opening (106) in the end plate(13). A hose (20) carries the product to a point of use or storage.

The blowdown.

The blowdown arrives at the heat exchanger from the boiler through athird hose (19). It enters the heat exchanger through an opening (109)in the end plate (13). Then it flows through a hole (88) in all thesheets. The blowdown enters the first chamber (79) and other chambers(not shown) through openings (111) in the gasket (78).

As the blowdown streams through its chambers it gives heat to the feedliquid in the adjacent chambers. The blowdown leaves the heat exchangerthrough the third hole (87) from the bottom in every sheet, then flowsthrough an opening (112) in the end plate (13). A hose (15) carries itout of the system.

Performance Characteristics of the Stacked-Sheet Heat Exchanger.

The counterflow heat exchanger (11) shown in FIG. 4 heats thirty gallons(132 liters) of water per hour, raising its temperature from 60° F. to207° F. (from 16° C. to 97° C.). Like the core of FIG. 2, thestacked-sheet heat exchanger achieves a high energy multiplier. Ittransfers 36,603 BTU (10.7 kwh) of heat energy from the product and theblowdown into the feed liquid every hour. The input energy required tomove the liquids through the heat exchanger is 3.3 watt hours, or 11.2BTU. The ratio of transferred energy to input energy is 3268 to 1.

Since the pressure drop across the heat exchanger is only one p.s.i.(0.07 kg/sq cm), the force of gravity is sufficient to cause liquids topass through it. Alternatively one could use a simple pump. If the pumpwere 25% efficient, the total energy required to move the liquidsthrough the heat exchanger would come to 45 BTU (13.2 watt hours). Inthis case the ratio of transferred energy to energy input would be 813to 1.

Another way of measuring the effectiveness of the counterflow heatexchanger (11) is to compare its actual performance with the theoreticallimit. The heat exchanger (11) of FIG. 4 raises the temperature of thefeed liquid by 147° F., from 60° F. to 207° F. (by 81° C., from 16° C.to 97° C.). The highest temperature the feed liquid could possibly reachis 212° F., (100° C.), which is the temperature of the product and theblowdown as they enter the heat exchanger. This heat exchanger, thenheats the cooler liquid to within 5° F. (3° C.) of the theoreticallimit. This 5° F. difference between the actual and the theoretical isknown as the "approach temperature." The ratio of the total temperatureshift of the cooler liquid to the approach temperature is a measure ofthe heat exchanger's performance. In this heat exchanger the ratiobetween the actual temperature shift of the feed liquid and the approachtemperature is 147 to 5, or 29 to 1. (Using degrees centigrade, theratio is 27 to 1).

An even higher standard of performance can be achieved by adding moresurface area for the same flow rate. If the number of sheets weredoubled, the approach temperature would be reduced by half. In this casethe ratio between the actual temperature shift and the approachtemperature would be twice as great, or 48 to 1.

Design Criteria for the Stacked-Sheet Heat Exchanger.

Extensive surface area is the key to efficiency. Like the otherembodiments of this invention, the stacked-sheet heat exchangers provideat least 2 square feet of heat transfer surface area for each gallon perhour (0.8 sq m/liter/hr) of cooler fluid passing through. The heatexchanger of FIG. 4 uses approximately 90 square feet (8.37 sq m) ofsurface area to heat 30 gallons (132 liters) of liquid per hour, a ratioof 3 square feet per gallon per hour (1.2 sq m/liter/hr).

With so much surface area available, the liquids can exchange heatreadily even though they flow with low velocities (less than 1 foot persecond, or 0.3 meters per second), low pressure heads (less than 1p.s.i., or 0.07 kg/sq cm), and a laminar flow pattern. (Laminar flow issmooth and orderly, with individual molecules tending to follow the samepaths.) The advantages of this gentle approach have already beenmentioned: little energy is required to move the liquids through theirchambers, the smoothly flowing liquids dissipate little energy inturbulence, the sheets transferring heat may be very thin, and thesheets may be placed very close together for optimal heat transfer.

In distillation the counterflow heat exchanger (11) should raise thetemperature of the the feed liquid high enough so available waste heatfrom the compressor motor can bring its temperature all the way to theboiling point. The counterflow heat exchangers of the invention meetthis requirement with simple, compact, inexpensive hardware.

Removal of Dissolved Liquids and Gases.

The ability of the heat exchanger (11) to heat the feed liquid nearly toits boiling point offers another important advantage: a convenient wayto remove toxic gases and liquids dissolved in the impure water. Ifthese gases and liquids are allowed to enter the boiler they go off withthe steam and contaminate the distilled water. The heat exchanger helpsto remove dissolved gases and liquids because the water can't hold themin solution as it approaches its boiling point. The liquids vaporize,and both the gases and liquids form bubbles. A gas-liquid separator inthe feed line between the heat exchanger (11) and the core (12) willallow the bubbles to rise from the water, thereby removing the toxicsubstances. In its simplest form the separator is an exit pipe toatmosphere with a valve to allow the exhaustion of gases except when theliquid level nears the outlet, at which time the valve closes. Agas-liquid separator is valuable for removing trihalomethanes or otherpoisonous gases from tapwater, for removing carbon dioxide from seawaterto help reduce scale formation, and for removing any non-condensiblegases to keep them from slowing down the condensation process.

Other Applications for the Heat Exchanger.

Although the counteflow heat exchangers shown in the drawings are allthree-fluid heat exchangers appropriate for distillation, otherembodiments of the invention could easily accomodate any number ofliquids for different applications. Many applications exist fortwo-fluid counterflow heat exchangers. In homes, for example, heatexchangers can capture heat from hot water leaving the shower, theclothes washer, or the dish washer, and transfer that heat into the coldwater from the city water pipes. The energy requirements of hot waterheaters will drop drastically if people feed heated water instead ofcold water into them. There are also many industrial applications forheat exchangers, and still more applications will be found as energyefficiency becomes more important.

This discussion will now turn to another still, similar to thestacked-sheet model in its structure and function but different in itsappearance and construction techniques.

The spiral still

FIG. 5 shows two more embodiments of the invention suitable forpurifying liquids: a spiral core (114) and a spiral counterflow heatexchanger (116).

The spiral core.

The core (114) of FIG. 5 is constructed from two sheets of stainlesssteel (type 316) wrapped around each other to form two spiral-shapedchambers: a boiler (100) and a condenser (105) in heat exchangerelationship. The sheets are 25 feet long, 1 foot wide, and 0.01" thick(5.1 m×0.3 m×0.25 mm). Spacers keep the sheets 0.06" (1.52 mm) apart.Gaskets (115) seal the chambers. The sheets transfer heat from vaporscondensing on one side into a liquid boiling on the other.

The spiral heat exchanger.

The heat exchanger (116) of FIG. 5 is built from three sheets ofstainless steel. Each sheet measures 32 feet by 1 foot by 0.01" (9.8m×0.3 m×0.25 mm). They wrap around each other to form threespiral-shaped chambers for the feed liquid, the product, and theblowdown. Spacers keep the sheets 0.032" (0.81 mm) apart. Gaskets (110)seal the chambers. The sheets transfer heat from hot liquid on one sideinto the cold liquid on the other.

The Relative Importance of the Specifications.

In the spiral core (114) and heat exchanger (116) the most significantstructural dimensions are the thickness of the sheets and the distancebetween them. The thickness of the sheets must be within the range of0.001" to 0.02" (0.025 mm to 0.51 mm). The separation between the sheetsmust be within the range of 0.005" to 1.0" (0.13 mm to 2.54 cm) in thecore, and within the range of 0.005" to 0.25" (0.13 mm to 6.4 mm) in thecounterflow heat exchanger. The sheets may be constructed from stainlesssteel, aluminum, glass, polyester, or any other material that can beformed into a thin sheet and maintain its structural integrity atoperating temperatures. The length and height of the sheets are notcritical, except that the amount of surface area determines flow rateand efficiency. Any standard gasket material would be suitable.

Design Strategy and Performance Characteristics of the Spiral Still.

The design strategy and performance characteristics are nearly identicalto those of the stacked-sheet stills. Both the spiral core (114) and thespiral counterflow heat exchanger (116) supply extensive surface areafor heat tranfer, slightly more than three square feet per gallon perhour (1.2 sq m/liter/hr). With extensive surface area in the core (114),the vapors can condense readily with only a small compression step. Thespiral core (114) purifies fifteen gallons per hour (66 liters/hr) witha compression step of 1 p.s.i. (0.07 kg/sq cm). With extensive surfacearea in the counterflow heat exchanger (116), the liquids can exchangeheat readily even though they flow gently. The spiral heat exchanger(116) heats thirty gallons (132 liters) of water per hour from 60° F. to206° F. with a pressure drop of 1 p.s.i. across the chambers (from 16°C. to 97° C. with 0.07 kg/sq cm).

The Paths of Liquids and Vapors through the Spiral Still: The feedliquid.

The feed liquid enters the central chamber of the heat exchanger (116)through the opening (117) at the lower right of the drawing. It receivesheat from the product and the blowdown as it winds through the turns ofthe spiral. Then the feed liquid flows through a hose (118) from theheat exchanger to the core (114). This hose (118) connects with metaltubes (119) which spill the feed liquid near the top of the boiler(100). Inside the boiler (100) the feed liquid receives heat from vaporscondensing on the opposite sides of the sheets and boils.

The vapors.

A compressor (121) driven by a motor (122) draws vapors out at the topof the boiler (100). First the vapors enter a demister (123). Thedemister (123) consists of a series of baffles--it leads the vapors in atortuous path to prevent them from carrying any entrained droplets ofliquid into the condenser (105). (In most applications a demister willnot be necessary. In seawater distillation, for example, the spiralstill reduces the total dissolved solids from 35,000 parts per millionto fewer than 3 parts per million without a demister. A demister wouldbe important only when extremely pure water is needed, for example inmanufacturing computer parts.) The compressore (121) compresses thevapors, then blows them through the compressor manifold (124) into thecondenser (105). (The compressor manifold (124) rests on the core andthe compressor when the core is in operation--the drawing elevates themanifold to reveal the compressor and the openings in the seals.) Whenthe compressed vapors enter the condenser (105) and touch the heattransfer sheets, they condense and give up their heat. This heat flowsthrough the sheets to boil the liquid on the other side.

The product and the blowdown.

The distilled liquid drips down the walls of the condenser (105). A hose(126) carries it from the condenser (105) to the heat exchanger. Anotherhose (127) carries blowdown from the boiler (100) to the heat exchanger.

Advantages and Disadvantages of the Spiral Configurations.

The spiral configurations are easier to build in some respects--there isno need to cut the sheets into small sections, to punch holes, or tomake complicated gaskets. But the spirals have two main disadvantages:it's difficult to seal them, and it's difficult to disassemble them forcleaning.

Vacuum distillation

By drawing a vacuum on any spiral or stacked-sheet core one can boil thefeed liquid at a lower temperature. Vacuum distillation offers threemain advantages:

(1) Vacuum distillation of seawater can reduce scale formation. Hardscale forms only at temperatures above 185° F. (85° C.). At lowertemperatures only soft scale forms. Soft scale is much easier to remove.By drawing enough of a vacuum to boil the seawater at 185° (85° C.) or alower temperature one can eliminate hard scale entirely.

(2) Vacuum distillation sometimes makes it possible to capture the wasteheat from the compressor motor. This waste heat can be captured bypassing the heated feed liquid through a metal coil wrapped around thecompressor motor. But the heated feed liquid must be cooler than themotor because heat will only flow from hot to cold. In somecircumstances a vacuum will lower the boiling temperature of the liquidbelow the operating temperature of the motor.

(3) By drawing a vacuum one can distill liquids at ambient temperature,in which case a heat exchanger would not be necessary. In large-scalesituations it might be valuable to eliminate the capital costs of theheat exchanger.

To this point the discussion has focused on water distillation, aprocess in which only one liquid will vaporize (unless traces of asecond liquid are dissolved in the water). Next it will examine how theinvention performs in a distillation process in which two liquids willvaporize.

Alcohol Distillation

The goal of this process is to separate alcohol from water. Nature givesa mixture of alcohol and water when plants ferment. Since alcoholevaporates more easily than water, it is possible to concentrate thealcohol by distilling the mixture.

The Hardware.

The cores and heat exchangers shown in FIGS. 1, 2, 3, 4, and 5 willdistill alcohol with no adaptation or adjustment.

The Process.

The invention distills alcohol with the same energy--recycling processit uses to purify water. The feed liquid is a mixture of alcohol andwater. In the alcohol fuel industry this mixture is commonly called"beer." The beer enters a heat exchanger, where it receives heat fromthe product and the blowdown. Then it enters a boiler, where it receivesheat from condensing vapors and boils. Both alcohol and water evaporate,but alcohol evaporates preferentially.

A compressor blows alcohol and water vapors from the boiler to thecondenser. The vapors condense on a thin sheet and give up their heat.This heat flows through the sheet to boil the beer on the other side.The condensed liquid has a higher concentration of alcohol than theoriginal beer. This product liquid, the distilled alcohol, leaves thecondenser and flows through a heat exchanger to give heat to incomingbeer.

The blowdown, the liquid remaining in the boiler, is a mixture ofalcohol and water with a lower concentration of alcohol than the beer.The blowdown also enters the heat exchanger to give heat to the incomingbeer.

Specifications Unique to Alcohol Distillation.

This method of distilling alcohol differs from the method of purifyingwater described earlier in two important respects--first, alcoholdistillation requires a slightly higher pressure step, within the rangeof 1 to 8 p.s.i. (0.07 to 0.56 kg/sq cm). The higher pressure step isneeded because there are two vapors (alcohol and water) in thecondenser. Until 1 to 8 p.s.i. (0.07 to 0.56 kg/sq cm) of compression isadded, neither alcohol vapors nor water vapors may have enough pressureto condense. Second, the temperature difference between the boilingsurfaces of the heat transfer sheets and the boiling liquid is greaterin alcohol distillation, up to 15° F. (8° C.). This higher temperaturedifference is a result of the higher compression step.

Compressing the vapors and recycling their heat is a novel approach toalcohol distillation. It reduces the energy requirements of the processmore than tenfold. The design of the heat exchanger and the core leadsto high efficiency for all the same reasons explained earlier withreference to water purification.

Operating Conditions.

Three passes are usually required to distill fuelgrade alcohol from afermentation product. Assuming the fermentation product contains 15%alcohol, the first distillation may employ a compression step of 7p.s.i. (0.49 kg/sq cm) and increase the alcohol to 35%. The seconddistillation may compress the vapors by 5 p.s.i. (0.35 kg/sq cm) andraise the alcohol content to 60%. The third pass may involve 7 p.s.i.(0.49 kg/sq cm) of compression and bring the mixture to 75% alcohol.Alcohol distillation may also be performed at a vacuum, either toeliminate the need for a heat exchanger or to capture the waste heatfrom the compressor motor.

Separation of Alcohol and Water in the Condenser.

A second method of alcohol distillation separates alcohol from water inthe condenser as well as the boiler. By compressing the vapors slightly,within the range of 1 to 4 p.s.i. (0.07 to 0.28 kg/sq cm), one cancondense water vapors selectively in the first distillation. (Watervapors condense more easily than alcohol vapors in the firstdistillation because they have a much higher percentage of the totalvolume of vapors. They have a higher percentage of the volume becausethe beer is mostly water and because water expands two-and-a-half timesas much as alcohol when the two evaporate.) With a compression step inthe range of 1 to 4 p.s.i. (0.07 to 0.28 kg/sq cm) the water vaporscondense readily, but the alcohol vapors still don't have a high enoughpressure to condense. By collecting the uncondensed vapors leaving thecondenser and condensing them separately, one can obtain analcohol-water mixture with a higher concentration of alcohol than thevapors which rose from the boiling beer. This method requires slightlymore energy than the method described earlier because the energy of theuncondensed vapors cannot be recycled. But this method separates alcoholfrom water more effectively in the first distillation.

The next process differs from alcohol distillation and waterpurification in that the main product is the substance that won't boiloff.

Dehydrating and Concentrating Liquids

The goal of these distillation processes is to boil off a liquid tocollect what remains. In most cases the liquid to be removed is water.Dehydrating means removing all the water; concentrating means removingsome of the water. In alcohol fuel production these processes arevaluable for concentrating fruit juices before fermentation and fordehydrating residues in the blowdown. The invention will also dehydratethe watery residues of food processing plants, industrial wastewater,and raw sewage.

If the liquid to be concentrated is not too viscous, the invention willconcentrate it in a continuous flow. The cores and heat exchangers shownin FIGS. 1, 2, 3, 4, and 5 concentrate liquids with the same procedurethey use to purify water--the only difference is that the "blowdown"from the boiler becomes the main product, and the distilled water fromthe condenser becomes a valuable by-product. No changes are required inthe hardware. The method and the performance characteristics are alsothe same as in water purification, except that compression requirementswill increase if a high concentration of the liquid is desired. Byrecycling heat efficiently this invention reduces the energyrequirements for concentrating liquids up to 99%.

Whenever the liquid is too viscous for a continuous flow process it ispossible to concentrate or dehydrate one batch of it at a time. FIG. 6shows a core for a batch process.

The batch dehydrator/concentrator

FIG. 6 is a cutaway drawing of a batch dehydrator/concentrator. A foldedcore (128) lies inside a vat (129). The vat (129), serving as a boiler,contains a mixture of solids and liquids to be separated. A lid (131)rests atop the vat (129). A compressor (125) and compressor motor (132)fasten to the lid (131).

The core (128) is built by folding a single sheet of stainless steelmany times to create an alternating sequence of boiling and condensingchambers in heat exchange relationship. The sheet is fifty feet long,twelve inches wide, and 0.01 inches thick (15.2 m×0.3 m×0.254 mm).Gaskets maintain a separation of 0.06" (1.52 mm) between the folds. Eachvertical section of the sheet transfers heat from condensing vapors onone side into the boiling liquid on the other.

The thickness of the sheet and the spacing between the folds are themost important structural dimensions. The thickness of the sheet mayrange from 0.001" to 0.02" (0.025 mm to 0.51 mm). The distance betweenthe folds may range from 0.005" to 1.0" (0.13 mm to 2.54 cm). The sheetmay be constructed from the same broad range of materials described withreference to the other cores. The specific gasket material isunimportant.

The Process.

This section explains briefly how the batch dehydrator/concentrator ofFIG. 6 can dehydrate watery wastes of food processing plants. The firststep is to bring the wastewater to a temperature near its boiling point.This may be accomplished either by heating the wastewater or by drawinga vacuum on the vat (129). (In either case it will be necessary to addor remove small amounts of heat to maintain the desired operatingconditions.) Once the wastewater is in the vat (129), the next steps arelowering the core (128) into the vat (129) and fastening the lid. Thewastewater can't get into the condensing chambers because they're sealedon the sides and at the bottom. But it enters the boiling chambers,which are open at the bottom.

The compressor compresses the steam from the boiling chambers by 1p.s.i. (0.07 kg/sq cm), then blows it into the condensing chambers. Whenthe compressed steam touches the condensing surfaces of the heattransfer sheet it condenses at a temperature hotter than the boilingliquid. Its heat flows through the sheet to boil the wastewater on theother side.

The condensed liquid is pure distilled water. It flows through a hole atthe bottom of the sheets and into a tube (133) which carries it out ofthe system. (The distilled water will flow upward for a few inchesbecause of the slight pressure increase in the condenser.)

After the wastewater has boiled off, the solids remain in the vat (129).They may be collected easily after the lid (131) has been lifted and thecore (128) has been removed. Any solids remaining in the boilingchambers can be blown out with compressed air.

Cross-Sectional Views of the Batch Dehydrator/Concentrator.

The next two drawings offer detailed views of the inside of this core:FIG. 7, a cross-sectional drawing of a boiling chamber, and FIG. 8, across-sectional drawing of a condensing chamber. Both drawings show thevat (129), the lid (131), the compressor (125), and the compressor motor(132). The gaskets are the only parts of FIGS. 6 and 7 that differ. Thegaskets (130) in the boiling chamber are open on the top and bottom; thegaskets (135) in the condensing chamber are open on the sides.

Arrows in FIG. 7 show how steam flows out the top of the boilingchambers into the compressor. The narrow strip of gasket material atthetop of the boiling chambers is a demister (134). The demister (134)forces the steam to flow to either side a short distance before it canreach the compressor (125). This short diversion makes it more difficultfor the steam to carry away any droplets of liquid.

Arrows in FIG. 8 show the path of the steam from the compressor (125)into the condensing chamber. The steam condenses on the heat transfersheets. The distilled water flows out of the condensing chambers througha hole (136) in the bottom of the sheets. In the boiling chambers (FIG.7) the gasket forms a barrier (137) around this hole to keep thedistilled water out of the boiling chambers as it leaves the core.

The small pieces of gasket on the sheet are spacers (140) to keep thefolds apart at any pressure from a complete vacuum to two atmospheres.

Performance Characteristics of the Batch Dehydrator/Concentrator.

The Batch Dehydrator-Concentrator of FIG. 6 removes liquid from aconcentrated solution at the rate of fifteen gallons (66 liters) perhour. The pressure step required depends on how concentrated thesolution is. The more concentrated the solution in the boiler, the lowerits vapor pressure, and the more work the compressor has to do to movesteam uphill into the high-pressure area of the condenser. Assuming acompression step of 2 p.s.i. (0.14 kg/sq cm) with a 50% efficientcompressor driven by a 50% efficient motor, the ratio of recycled energyto actual input energy is approximately 25 to 1. Higher energymultipliers can be achieved by increasing the heat transfer surface areaor by using a more efficient compressor and compressor motor.

Although the process described above is applicable only to liquids, asimilar dehydration process will remove moisture from solids.

Drying Solids

The goal of this distillation process is to remove a liquid from a wetsolid--for example, to dry clothing, fruits, vegetables, or distillers'grains. The invention recycles energy by evaporating the liquid,compressing its vapors, condensing the vapors on a thin sheet ofmaterial, and recycling heat from the condensing vapors back into theevaporator to dry the solids.

The batch dehydrator

FIG. 9 is a cutaway drawing of a batch dehydrator. It consists of acurved stainless steel heat transfer sheet (138) inside a cylindricalcase (139). The sheet measures ten feet long, three feet wide, and 0.01"thick (3.04 m×0.91 m×0.254 mm). The area inside the curved sheet servesas a boiler or evaporator (147)--a receptacle for the solids to bedried. The area between the sheet (138) and the case (139) serves as acondenser. A compressor (141) and compressor motor (145) are mounted onthe end.

The heat transfer sheet (138) may be constructed from any material whichcan be formed into a thin sheet and maintain its structural integrity atthe operating temperatures. For best results the thickness of the sheetshould be within the range of 0.001" to 0.02" (0.025 mm to 0.51 mm). Thelength and width of the sheet may vary depending on the quantity ofgrains or clothing to be dried.

The Process.

This section explains how the batch dehydrator dries clothing (or anyother wet solids). The first steps are inserting a load of wet clothingthrough the front opening (142) and closing the door (143). The nextstep is adding heat or drawing a vacuum to begin evaporating the water.The compressor (141) draws the water vapor (steam) through a small hole(144) at the end of the evaporator. Then it compresses the vapor by 1p.s.i. (0.07 kg/sq cm) and blows it around to the other side of thesheet.

When the compressed water vapor strikes the condensing surface of theheat transfer sheet it condenses at a temperature hotter than theclothing. Its heat flows through the heat transfer sheet into theevaporator to dry the clothing. The condensed liquid leaves thecondenser through a hole (146) at the bottom of the case.

Other Views of the Batch Dehydrator. FIG. 10 shows the batch dehydratorof FIG. 9 in a cross-sectional view from the end. The heat transfersheet (138) and the case (139) are shown, as are the evaporator (147),the condenser (148), and the hole (146) where distilled water drainsfrom the condenser.

FIG. 11 shows the same batch dehydrator in a cross-sectional view fromthe side. This drawing shows the heat transfer sheet (138), the case(139), the front opening (142) where the solids are inserted, the hole(144) where the compressor draws out the steam, and the hole (146) atthe bottom of the case where distilled water leaves the condenser.

Other Considerations for High Efficiency.

For optimal efficiency in drying solids, it's necessary to do three morethings:

1. Remove non-condensible gases. If air or other non-condensible gasesare allowed to accumulate in the condenser they will slow down thecondensation process. The easiest way to remove non-condensible gases isto draw a vacuum on the core from the outlet to the condenser.

2. Maintain thermal balance. It will be necessary to add or remove smallamounts of heat to maintain the desired operating conditions.

3. Keep the wet solids in close contact with the heat transfer sheet.For this reason it's advisable to rotate the batch dehydrator like aconventional clothes dryer. The solids dry by tumbling against theevaporation surface.

Performance Characteristics of the Batch Dehydrator.

The dehydrator of FIG. 9 will accept a ten-pound (4.5 kg) load of wetclothing. The fabric makes up six pounds (2.7 kg) of the load, andmoisture makes up the other four pounds (1.8 kg). The dehydrator driesthe clothing in thirty minutes. It recycles 3840 BTU (1.13 kwh) of heatenergy to evaporate the four pounds (1.8 kg) of water. The theoreticalenergy input required to compress the water vapor by 1 p.s.i. is 18 BTU(5.3 watt hours). The ratio of the recycled energy to the theoreticalinput energy is 3840 to 18, or 213 to 1. Assuming the compressor is 50%efficient and the compressor motor is 50% efficient, approximately 72BTU (21.2 watt hours) of energy will be required to compress the steam.Under these circumstances, the ratio of recycled energy to actual inputenergy will be slightly greater than 50 to 1.

Design Criteria for the Batch Dehydrator.

The most important design consideration for the batch dehydrator isextensive heat transfer surface area for the flow rate of distilledwater--at least two square feet each for gallon of fluid evaporated perhour (0.8 sq m/liter/hr). The dehydrator of FIG. 9 supplies thirtysquare feet per gallon per hour (12 sq m/liter/hr).

The final application of this invention, unlike the others, is not aseparation process at all. It might be called a mixing process--it mixesliquids of different salinities to capture the energy that is released.

Power Generation

The goal of this distillation process is to generate a head of steam fordoing useful work. The invention recycles energy to sustain the boilingaction.

The Process.

The apparatus boils fresh water to generate a head of steam. The steamspins the blades of a turbine. An electrical generator linked to theturbine converts the rotary motion into electricity. Then the steamcondenses in hot concentrated brine and gives up its heat. This heatflows through sheets of material to boil the fresh water on the otherside. The diluted brine flows from the condenser to a heat exchanger,where it gives heat to incoming fresh water and salt water.

This process requires that the boiler be a high pressure area relativeto the condenser, so steam will naturally flow from the boiler to thecondenser. But it also requires that the condenser be a high temperaturearea relative to the boiler, so heat will naturally flow from thecondenser to the boiler Both these conditions are met by introducingfresh water into the boiler and concentrated brine into the condenser.The dissolved salts lower the steam pressure of the brine. Its steampressure remains lower than that of the fresh water, even when the brinebecomes slightly hotter.

The power generator

FIG. 12 is an exploded drawing of a stacked-sheet core for generatingpower. This core was built by stacking together 51 heat transfer sheetsmade of stainless steel type 316. The sheets measure 12"×16"×0.01" (0.3m×0.4 m×0.25 mm). Gaskets maintain a separation of 0.06" (1.52 mm)between the sheets. The areas between the sheets serve as chambers forboiling the fresh water and for condensing its vapors in hot salt water.Boiling chambers and condensing chambers alternate. Each sheet transfersheat from the hot salt water on one side into the boiling fresh water onthe other.

The Relative Importance of the Specifications.

As in the other cores, the important structural dimensions which definethe invention are the thickness of the sheets and the distance betweenthem. The thickness of the sheets must be within the range of 0.001" to0.02" (0.025 mm to 0.51 mm). The distance between the sheets must bewithin the range of 0.005" to 1.0" (0.13 mm to 2.54 cm). The sheets maybe constructed from the same range of materials described with referenceto FIG. 1. The height and width of the sheets are not critical. Thenumber of sheets depends on the desired flow rate. The turbine may bereplaced by a positive displacement piston or any other means ofconverting vapor flow into mechanical motion.

The Sheets and the Chambers.

FIG. 12 exposes two heat transfer sheets (149 and 151). Both sheets havea gasket affixed to one surface. The sheet (149) on the right has agasket (152) to form a boiling chamber (153). The boiling chamber (153)lies between the sheet (152) and the front end plate (154). (Within thestack the boiling chambers lie between successive heat transfer sheets.)The boundaries of the boiling chamber (153) are defined by referencenumbers (182) at the top, (193) at the bottom, (168) at the left, and(202) at the right. The sheet (151) on the left has a gasket (156) toform a condensing chamber (157). The condensing chamber (157) liesbetween the two heat transfer sheets (149 and 151). Its boundaries areindicated by reference numbers (184) at the top, (194) at the bottom,(169) at the left, and (203) at the right.

The other prominent elements of the drawing are a turbine (158), apressure switch (159), and the rear end plate (161).

Paths of Liquids and Vapors through the Core of FIG. 12.

This section will explain how salt water enters the condensing chambers,fresh water enters the boiling chambers, steam flows from the boilingchambers to the condensing chambers, and diluted salt water leaves thecondensing chambers.

The salt water.

The salt water arrives at the core in a hose (162) at the left of thefront end plate (154). (If a heat exchanger is in use, the salt waterwill have already been heated by diluted water leaving the process.) Aheater (163) connected to this hose (162) adds small amounts of heatintermittently to maintain the desired operating conditions.

The heater (163) is controlled by a pressure switch (159) sensitive tosteam pressure in the condenser. The pressure switch (159) communicateswith the condenser through a hose (150), an opening (155) in the endplate, and holes (160) 1" (2.54 cm) in diameter in the sheets. When thesteam pressure drops too low the switch (159) closes, completing acircuit so power can flow to the heater (163). When the steam pressurebecomes high enough, the switch (159) opens, breaking the circuit andshutting off power to the heater (163).

The salt water enters the core through an opening (164) in the endplate, then flows through holes (166) 1" (2.54 cm) in diameter in allthe sheets. Gaskets form a seal (167) to keep the liquids and vaporsinside the system. The salt water can't enter the boiling chambers (153)because the gaskets form barriers (168). But it enters each condensingchamber (157) through openings (169) in the gaskets (156). The saltwater partially fills each condensing chamber (157). A spill tube (171)regulates the height of the salt water so it covers the entire surfaceof the sheets.

The fresh water.

Fresh water approaches the core in a hose (172) to the right of the endplate (154). (If a heat exchanger is being used, the fresh water hasalso been heated to a temperature near its boiling point by the outgoingdiluted salt water.) The fresh water streams into the core through anopening (173) in the end plate (154), then flows through holes (174) 1"(2.54 cm) in diameter in the lower corners of each sheet. The freshwater can't enter the condensing chambers (157) because the gaskets(156) form a barrier (176). But it enters each boiling chamber (153)through an opening (177) in the gaskets (152) and spreads evenly acrossthe boiling surfaces of the heat transfer sheets. The fresh waterpartially fills each boiling chamber (153), its height regulated by aspill tube (178) so it covers the entire boiling surface when it boils.

Fresh water from the boiling chambers (153) seeks its own level in thespill tube (178) assembly. The fresh water flows through an opening(170) in the gaskets and through holes (165) in the sheets. The gasketforms a barrier (190) to keep the fresh water out of the condensingchambers. Then the fresh water flows through an opening (180) in the endplate and into a hose (185) containing the spill tube (178). A secondhose (175) connects the spill tube with the top of the boiling chambersto provide a pressure reference. Steam from the boiling chambers entersthis hose (175) through holes (195) in the sheets and an opening (179)in the end plate. Any fresh water overflow falls through the spill tube(178) and into a hose (181). This hose (181) carries the fresh wateroverflow to the heat exchanger, where it joins the diluted salt water togive heat to the incoming fresh water and salt water.

The steam.

Inside each boiling chamber (153) the fresh water receives heat from hotsalt water on the opposite sides of the sheets. The fresh water boilsand steam rises. The steam expands toward the low-pressure area in thecondensing chambers (157). It rushes out of each boiling chamber (153)through an outlet manifold (182) at the top. Then the steam flowsthrough holes (183) half an inch in diameter at the top of each sheet onits way out of the core. As it exits, a barrier (184) keeps it out ofeach condensing chamber.

The steam rushes through an opening (186) in the end plate (154) andenters an expander (201). The expander consists of a small manifold(187), two hoses (188 and 189), and a turbine (158). The expanding steamspins the turbine blades, just like a wind spins a windmill. Thespinning motion of the turbine can generate electrical power, pumpwater, or do other useful work.

The second hose (189) carries steam from the turbine back into the core.The steam flows through through an opening (191) in the end plate (154)and through holes (192) 1/2" (1.27 cm) in diameter at the bottom ofevery sheet. The steam can't enter the boiling chambers (153) becausethe gasket (152) forms a barrier (193). But the steam enters eachcondensing chamber (157) through an inlet manifold (194) formed by thegasket (156). This inlet manifold (194) contains many small openings,the pressure drop across each opening being great enough so steam enterseach opening at an equal rate. As a result steam spreads evenlythroughout the salt water in the condensing chambers (157).

When the steam contacts the hot salt water it condenses and gives up itsheat. This heat raises the temperature of the salt water in thecondensing chambers (157), making it hotter than the fresh water in theboiling chambers (153). Heat from the salt water flows through thesheets to boil the fresh water on the other side. The boiling freshwater generates more steam, and the cycle continues.

The diluted salt water.

The diluted salt water leaves the condensing chambers (157) throughopenings (203) in the gasket. It flows through holes (196) 1" (2.54 cm)in diameter in the sheets on its way out of the core. Barriers (202)prevent the diluted salt water from entering the boiling chambers. Itpasses through an opening (197) in the end plate (154), then enters ahose (198) which carries it to the heat exchanger, if a heat exchangeris in use.

Other Details of FIG. 12.

The tiny sections of gasket in the central area of the sheets arespacers (204) to hold the sheets apart at any pressure from a completevacuum to two atmospheres. Assembly holes (199) in the sheets andassembly holes (200) in the end plates are intended for bolts (notshown) to hold the core together.

Counterflow Heat Exchange.

The power generation process may use the heat exchanger shown in FIG. 4.In this case the heat exchanger heats cold fresh water and cold saltwater to temperatures near their boiling points by capturing heat fromhot diluted salt water leaving the core. The liquids flow through theirchambers with low velocities (less than 1 foot per second, or 0.3 metersper second), low pressure heads (less than 1 p.s.i. or 0.07 kg/sq cm),and laminar flow patterns. Instead of using a heat exchanger it would bepossible to draw a vacuum on the core to boil the fresh water at ambienttemperature.

Design Criteria for the Power Generator.

Like all the other embodiments of the invention, the power generator isa form of heat exchanger. The most important aspect of its design isextensive surface area for heat exchange. The power generationembodiments supply at least two square feet of heat transfer surfacearea for every gallon of fresh water evaporated per hour (0.8 sqm/liter/hr). The embodiment shown in FIG. 12 supplies approximatelythree square feet of surface area per gallon per hour (1.2 sqm/liter/hr).

Performance Characteristics of the Power Generator.

This power generator evaporates fifteen gallons (66 liters) of freshwater per hour. When distilled water feeds into the boiling chambers andconcentrated brine feeds into the condensing chambers, a pressuredifference of 4.5 p.s.i. (0.32 kg/sq cm) between the boiler and thecondenser is created. It generates 750 watts of power, enough to supplyelectricity for the average residence.

Like the other embodiments of the invention, the power generatorrecycles energy efficiently with simple, easily manufactured hardware.By reducing the energy requirements of distillation and broadening thescope of its application, this invention will allow this ancient processto solve some of the most critical problems of contemporary humansocieties.

I claim the following inventions:
 1. A method of generating power usinga first liquid and a second liquid having a lower vapor pressure thansaid first liquid, said method comprising the step of:(a) providingmeans for defining a vertically extending boiling chamber and avertically extending condensing chamber on opposite sides of avertically extending common plate member which includes on one sidethereof, a specific boiling surface within and forming part of saidboiling chamber and, on the opposite side thereof, condensing surfacewithin and forming part of said condensing chamber and aligned with saidboiling surface, said plate member being sufficiently thermallyconducive an sufficiently thin in the area of said boiling andcondensing surfaces to conduct heat across the two surfaces relativelyefficiently; (b) directing a continuously replenished supply of saidfirst liquid into said boiling chamber so as to maintain said boilingchamber filled with said first liquid to a level which entirely coverssaid boiling surface when said first liquid is caused to boil andcausing the first liquid therein to boil, whereby it does so evenly oversubstantially the entire boiling surface of said plate member sufficientto produce vapor from some of said first liquid; (c) maintaining asupply of said second liquid within said condensing chamber at a highertemperature than the temperature of said boiling first liquid but at asufficiently low temperature so that the second liquid does not boil,said second liquid being maintained within said condensing chamber at alevel which completely covers said condensing surface; (d) convertingthe vapor from said boiling first liquid to mechanical energy; (e)thereafter condensing said vapors into said second liquid within saidcondensing chamber; thereby releasing heat within said last-mentionedchamber; and (f) transferring said heat from said second liquid to saidfirst liquid through said common plate member to sustain the boilingaction.
 2. A method according to claim 1 wherein said first liquid isfresh water and said second liquid is salt water.
 3. A method accordingto claim 1 wherein said plate member is planar in configuration.
 4. Amethod of generating power using a first liquid and a second liquidhaving a lower vapor pressure than said first liquid said methodcomprising the steps of:(a) providing means for defining a plurality ofalternating, directly adjacent vertically extending boiling andcondensing chambers separated by vertically extending plate members,each of which includes on one side thereof a specific boiling surfacewithin and defining one lateral boundary of a directly adjacentvertically extending, laterally narrow boiling chamber and on theopposite side thereof an aligned condensing surface within and definingone lateral boundary of a directly adjacent condensing chamber, each ofsaid plate members being sufficiently thermally conductive ansufficiently thin in the area of its boiling and condensing surfaces toconduct heat across the two surfaces relatively efficiently; (b)directing a continuously replenished supply of said first liquid intoeach of said boiling chambers so as to maintain said boiling chamberfilled with said first liquid to a level which entirely covers saidboiling surface when said first liquid is caused to boil and causing thefirst liquid therein to boil, whereby it does so uniformly and evenlyover each of the entire boiling surfaces of each plate member sufficientto produce vapor from some of said first liquid within said boilingchambers; (c) maintaining a supply of said second liquid within each ofsaid condensing chambers at a a higher temperature than the temperatureof said boiling first liquid but at a sufficiently low temperature sothat the second liquid does not boil; said second liquid beingmaintained within each of said condensing chambers at a level whichcompletely covers its associated condensing surface; (d) converting thevapor from said boiling first liquid in each boiling chamber tomechanical energy; (e) thereafter condensing said vapor into said secondliquid within each of said condensing chambers; thereby releasing heatwithin said last-mentioned chambers; and (f) transferring said heat fromsaid second liquid within each condensing chamber to said first liquidwithin the adjacent boiling chamber through the plate membertherebetween to sustain the boiling action.
 5. A method according toclaim 4 wherein said first liquid is fresh water and said second liquidis salt water.
 6. A method according to claim 4 wherein each of saidplate members is planar in configuration.